Introduction
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| Illustration 1 | g03809179 |
Typical example (1) Fuel strainer (2) Primary fuel filter (3) Electric transfer pump (4) Secondary fuel filter (5) Fuel Injection Pump (6) Inlet pressure regulator (7) Fuel manifold (rail) (8) Pressure relief valve (9) Electronic unit injector (10) Fuel cooler (if equipped) (A) Fuel tank | |
Fuel is drawn from the fuel tank through a fuel strainer to an external electric transfer pump. The fuel then flows to the 10 micron primary fuel filter and a water separator.
The fuel then flows to a 4 micron secondary fuel filter.
The fuel flows from the secondary fuel filter to a pressure regulator. A pressure regulator that is installed in the low-pressure fuel system controls the fuel pressure to the fuel injection pump.
From the pressure regulator, the fuel flows to the fuel injection pump. The fuel is pumped at an increased pressure of up to 200 MPa (29000 psi) to the fuel manifold (rail).
High Pressure Fuel System
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| Illustration 2 | g03809184 |
Typical example (1) Fuel injection pump (2) Fuel temperature sensor (3) Suction control valve for the fuel injection pump (4) Pressure relief valve (5) Electronic unit injector (6) Fuel manifold (rail) (7) Fuel pressure sensor (8) Fuel transfer pump | |
The fuel injection pump (1) feeds fuel to the high-pressure fuel manifold (rail) (6). The fuel is at a pressure of 200 MPa (29000 psi). A pressure sensor (7) in the high-pressure fuel manifold (rail) (6) monitors the fuel pressure in the high-pressure fuel manifold (rail) (6). The ECM controls a suction control valve (3) in the fuel injection pump (1) in order to maintain the actual pressure in the high-pressure fuel manifold (6) at the desired level. The high-pressure fuel is continuously available at each injector. The ECM determines the correct time for activation of the correct electronic unit injector (5) which allows fuel to be injected into the cylinder. The leakoff fuel from each injector passes into a drilling which runs along the inside of the cylinder head. A pipe is connected to the rear of the cylinder head in order to return the leakoff fuel to the fuel tank.
Components of the Fuel Injection System
The fuel injection system has the following mechanical components:
- Primary filter/water separator
- Electric transfer pump
- Fuel transfer pump
- Secondary fuel filter
- Fuel injection pump
- Fuel injectors
- Fuel manifold
- Pressure relief valve
- Fuel pressure sensor
- Fuel temperature sensor
The following list contains examples of both service and repairs when you must prime the system:
- A fuel filter is changed.
- A low-pressure fuel line is replaced.
- The fuel injection pump is replaced.
- The ECM is replaced.
For the correct procedure to prime the fuel system, refer to Systems Operation, Testing and Adjusting, "Fuel System - Prime".
Primary Filter/Water Separator
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| Illustration 3 | g03598437 |
Typical example | |
The primary filter/water separator (1) is located between the electric lift pump and the secondary fuel filter. The primary filter/water separator (1) provides a 10 micron filtration level.
Secondary Fuel Filter
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| Illustration 4 | g03598036 |
Typical example | |
The secondary fuel filter (1) is located after the primary fuel filter. The secondary fuel filter (1) provides a 4 micron filtration level.
Fuel Pump Assembly
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| Illustration 5 | g02216343 |
Typical example | |
The fuel pump assembly consists of a low-pressure transfer pump and a high-pressure fuel injection pump. The pump assembly is driven from a gear in the front timing case at engine speed. The fuel injection pump (1) has three plungers that are driven by a camshaft. The fuel injection pump (1) delivers a volume of fuel three times for each revolution. The stroke of the plungers are fixed.
The injector will use only part of the fuel that is delivered by each stroke of the pistons in the pump. The suction control valve (3) for the fuel injection pump (1) is controlled by the ECM. This maintains the fuel pressure in the fuel manifold (rail) at the correct level. A feature of the fuel injection pump (1) allows fuel to return to the tank continuously.
The fuel temperature sensor (2) measures the temperature of the fuel. The ECM receives the signal from the fuel temperature sensor (2). The ECM calculates the volume of fuel.
The fuel injection pump has the following operation:
- Generation of high-pressure fuel
The fuel output of the fuel injection pump is controlled by the ECM in response to changes in the demand of fuel pressure.
Shutoff
The engine shuts off by preventing the electronic unit injectors from injecting. The ECM then closes the suction control valve to prevent the pressure in the fuel manifold (rail) from increasing.
Control
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| Illustration 6 | g03809180 |
Typical example of the electrical control system for the fuel system (1) Electronic Control Module (ECM) (2) Fuel rail pressure sensor (3) Inlet manifold pressure sensor (4) Atmospheric pressure sensor (5) Coolant temperature sensor (6) Inlet manifold air temperature sensor (7) Secondary speed/timing sensor (8) Primary speed/timing sensor (9) Fuel injection pump (10) Suction control valve for the fuel injection pump (11) Fuel temperature sensor (12) Electronic unit injectors | |
The ECM determines the quantity, timing, and pressure of the fuel in order to be injected into the fuel injector.
The ECM uses input from the sensors on the engine. These sensors include the speed/timing sensors and the pressure sensors.
The ECM controls the timing and the flow of fuel by actuating the injector solenoid.
The amount of fuel is proportional to the duration of the signal to the injector solenoid.
The ECM controls the fuel pressure by increasing or decreasing the flow of fuel from the fuel injection pump.
Fuel Injectors
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| Illustration 7 | g02290433 |
Typical example (1) Electrical connections (2) Bolt (3) Clamp (4) Combustion washer (5) O-ring (6) Fuel inlet | |
Note: If a replacement electronic unit injector is installed, the correct injector code must be programmed into the electronic control module. Refer to Troubleshooting, "Injector Code - Calibrate" for more information. The code that is required is located at Position (X). Record Code (X) before the electronic unit injector is installed.
The fuel injectors contain no serviceable parts apart from the O-ring seal and the combustion washer. The clamp and setscrew are serviced separately.
When the ECM sends a signal to the injector solenoid, a valve inside the injector opens. The valve allows the high-pressure fuel from the fuel manifold to enter the injector. Fuel is also diverted via the leak-off route to cool and lubricate injector. The pressure of the fuel pushes the needle valve and a spring. The difference in pressure around the needle valve becomes too great, this causes the pressure to lift the needle and start injecting.
The timing and duration of injection is controlled by a solenoid valve in the injector. The valve has two positions. In the closed position, the valve closes the inlet to the injector. In this position, fuel above the injector needle is allowed to vent through the leakoff port.
In the open position, the valve opens the inlet to the injector. Simultaneously, the valve closes the leakoff port in order to allow high-pressure fuel to flow to the needle. When the solenoid valve is closed, some fuel escapes past the valve in order to vent through the leakoff port. A certain volume of fuel always flows from the leakoff port. If the volume of fuel increases beyond a critical level, the fuel injection pump will not be able to maintain pressure in the fuel manifold.
When the needle valve opens, fuel under high pressure will flow through nozzle orifices into the cylinder. The fuel is injected into the cylinder through the orifices in the nozzle as a very fine spray.
When the signal to the injector ends, the valve closes. The fuel in the injector changes to a low pressure. When the pressure drops the needle valve will close and the injection cycle stops.
The needle valve has a close fit with the inside of the nozzle. This makes a positive seal for the valve.
The electronic unit injectors can be instructed to inject fuel multiple times during the combustion process. A close pilot injection occurs before the main injection. The close pilot injection helps to reduce NOx and noise. The main injection period helps to increase the torque of the engine. The after injection period helps to reduce the amount of smoke that is produced.
Fuel Manifold
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| Illustration 8 | g01911496 |
Typical example | |
The fuel manifold (2) stores high-pressure fuel from the fuel injection pump. The high-pressure fuel will flow to the injectors.
The fuel pressure sensor (3) measures the fuel pressure in the fuel manifold (2) .
The pressure relief valve (1) will prevent the fuel pressure from getting too high.
The fuel pressure sensor must be replaced with the fuel manifold (rail). The pressure relief valve can be serviced as a separate component.